1. Field of the Invention
The present invention relates to an actuator which starts an operation of a device to which it is attached by generating an operation gas which is a combustion gas when activated and more particularly to, for example, an actuator which is preferably used for an onboard automotive safety apparatus such as a hood pop-up apparatus which lifts up a hood panel in receiving a pedestrian as a protection target.
2. Description of the Related Art
Some of conventional actuators like the one described above are used in a hood pop-up device which lifts up a hood panel, and those actuators are configured as a piston-cylinder type actuator which makes use of combustion gas generated as a result of ignition of explosive material when a gas generator is activated as operation gas (for example, refer to JP-A-2011-208738). In this actuator, the piston rod includes the piston portion which can slide within the cylinder and the rod portion which extends to the outside of the cylinder from the piston portion and which supports a hood panel as a receiving member which receives a pedestrian as a protection target in such a way as to raise the hood panel as high as a pedestrian receiving position. Further, due to the actuator being disposed in the hood panel, in this actuator, the packing is provided in the gap portion defined between near the distal end of the rod portion of the piston rod and the inner circumferential surface of the cylinder with a view to preventing the intrusion of rain water into the interior of the actuator. In case rain water arrives at the gas generator which supplies the operation gas to the piston portion side, the ignition fails when the gas generator is activated, and therefore, the provision of the packing is necessary with a view to ensuring the waterproofness of the actuator.
Further, in this actuator, the E ring is provided in the rod portion with a view to preventing the unintentional protrusion of the piston rod before actuation, that is, the unintentional extension of the actuator which is triggered by the forward movement of the piston rod before actuation. This E ring is brought into abutment with the ceiling wall portion of the cylinder to prevent the forward movement of the piston rod when in actuation while striking strongly the ceiling wall portion to be dislocated from the rod portion to allow the forward movement of the piston rod when the actuator is actuated.
In the conventional actuator, however, since the packing is provided, the packing has to be selected while considering the production tolerance in dimension, and the packing accommodation groove has to be designed accordingly. In addition, the E ring and the E ring accommodation groove also need to be provided, resulting in the problem that the actuator cannot be configured simple.